1. Field of the Invention
This invention relates to thermotropic polyesters derived from ferulic acid and to a process for preparing such polyesters.
2. Description of the Prior Art
It is known in the art that light sensitive polyesters may be prepared from cinnamic acid ##STR1## or its derivatives by reacting the acid or derivative with polyhydric alcohols and polycarboxylic acids. Thus, as described in U.S. Pat. No. 3,030,208, a light sensitive polyester may be prepared by polycondensing a polyhydric alcohol and a polycarboxylic acid with a cinnamic acid derivative having the formula: ##STR2## wherein R represents one or more alkyl, aryl, aralkyl, alkoxy, nitro, amino, carboxyl groups or halogen or hydrogen atoms and R' represents an OH group, a halogen atom, a hydrocarbon radical or an amine group. The light sensitivity of the polyester is derived from the cross-linkable double bond and makes the polyester particularly useful in the production of films or foils that may be used in the reproduction art.
The use of another cinnamic acid derivative, 2,5-dimethoxycinnamic acid or its lower alkyl ester, is disclosed in U.S. Pat. No. 3,600,357. As set forth therein, from about 0.01 mole percent to about 3.0 mole percent of the derivative is added to a copolyester prepared from a saturated dicarboxylic acid or its lower alkyl diester and a lower aliphatic glycol to impart optical brightness to fibers or films prepared from the copolyester.
Illustrative cinnamic acid derivatives employed in the preparation of polyesters and copolyesters and which exhibit optical anisotropy in the molten state are described in Netherlands Application No. 75,05551, filed May 1, 1975 which claims the priority of U.S. Application Ser. Nos. 468,690, 468,695 and 468,697, all filed on May 10, 1974. More particularly, the Netherlands Application discloses that p-acetoxycinnamic acid may be melt polymerized with various aromatic monomers to produce polyesters or copolyesters which may be formed into fibers, films or molded articles. A description of a number of related polyesters and copolyesters may also be found in U.S. Pat. No. 4,118,372 which is a Continuation-in-part of the aforementioned U.S. Application Ser. No. 468,697.
The homopolymerization of ferulic acid under experimental conditions is disclosed in the article by Y. Tanaka et al entitled "Polycondensation of Hydroxy-Trans-Cinnamic Acids Under High Pressure", Proc. Int. Conf. High Pressure, 4th, (1975) pp. 704-712. As the title suggests, the homopolymer is obtained by polycondensing the monomer at high pressures ranging from 10 to 80 kilobars and at temperatures ranging from 200.degree. to 450.degree. C. in the solid phase. The resulting homopolymer is described as being amorphous in nature.